Note: Descriptions are shown in the official language in which they were submitted.
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 1 -
METHOD FOR REMOVING CONDENSABLES FROM A NATURAL GAS
STREAM
FIELD OF THE INVENTION
The present invention relates to a method for
removing condensables from a natural gas stream and to a
well completion system for producing gas from a
subterranean formation wherein said method is applied.
BACKGROUND TO THE INVENTION
Natural gas, produced from a subsurface or sub-sea
gas producing formation (hereinafter subterranean
formation), requires the separation of components that
are normally liquid or that have relatively high
condensation temperatures. These components, which are
collectively referred to in the claims and the
description with the expression "the condensables"
include water, propane, butane, pentane, propylene,
ethylene, acetylene and others such as carbon dioxide,
hydrogen sulfide, nitrogen gas and the like. Typically,
the gas stream is treated, on surface, downstream of a
wellhead that is connected with a subterranean gas
producing formation via a primary wellbore containing a
tubing extending downhole from the wellhead.
This is not very cost-effective, in particular for
multilateral wells (i.e., well completion systems
comprising a multiple branched wellbore system connecting
the reservoir of a producing formation with one or more
other reservoirs) wherein the natural gas and/or the
condensables, or part of either, is re-injected from one
formation into another or within the formation from one
reservoir zone into another. This is done, for instance,
to stimulate a new well or revive an existing well; or to
store the natural gas or condensables for later use, etc.
29-01-2001 CA 02357635 2001-06-28 EP 009910497
~-2-
29. ol= Separators that are effective to lower dew points of
67 gases generally require complex equipment and
instrumentation, such as refrigerated sponge oils or
glycols absorbers. Such operations are generally too
complex to be placed at wellheads such as sea floor
wellheads, and too expensive to be placed at individual
wellheads in a gas producing field.
Downhole separators to remove water from gas as it is
being produced are known, for example in US-A-5,444,684.
This device uses floating balls that float up and block a
flowpath when a water level in the wellbore becomes high,
and then as gas pressure builds, and forces the water
level down, allowing production of gas that is free of
liquid water. This device is only capable of keeping
liquid water out of produced gas. It is not capable of
removing either condensables or water from the produced
gas.
US-A-5,794,697 also discloses a downhole separator
for taking gas from a mixture of liquids and gas produced
into a wellbore. This patent focuses on downhole
compression of the gas and re-injection of the gas into a
gas cap over the oil remaining in the formation. A
separator is shown and described as an auger that imparts
a swirling motion to the fluids, and then removal of the
gas from the center of the swirl. This separator also
does not lower the dew point temperature of the gas (i.e.
remove the condensables), but only separates existing
phases.
The separation method and inertia separator according
to the preamble of claims 1 and 7 are known from
International patent application WO 95/09970. The known
separator includes a cyclone in which produced water is
separated from the produced gas and water vapor is
separated from the gas in a separate high pressure
membrane.
AMENDED SHEET
CA 02357635 2007-04-12
- 2a -
It would be desirable to have a more simple separator
for removing condensables and/or water from a natural gas
stream upstream of the wellhead choke, i.e., before
entering surface or sub-sea facilities with typical lower
pressure ratings in the order of 15 MPa (15 MN/mZ) or less.
Firstly, this is because a higher pressure drop for
separation is still available upstream of the wellhead
choke, thereby making better use of the available potential
energy, which otherwise gets dissipated at the wellhead
choke. Secondly, this is because as gas flows up the
wellbore, it may be cooled by heat transfer to the more
shallow formations surrounding the wellbore, and by
adiabatic expansion of the gas as it flows up the well.
When the gas cools, the condensables and/or water may then
is condense from the previously saturated gas stream.
Condensed liquids in a gas producing borehole could cause
many problems. The separate liquid phase could
considerably increase the static head within the wellbore,
and therefore reduce the well head pressure and/or gas
production. Depending on the flow regime that results, the
liquids could build up until the bottom of the wellbore is
exposed to a considerable additional liquid head. Also,
water could combine with hydrocarbons and/or hydrogen
sulfide to form hydrates in the wellbore. These hydrates
could plug the well. To prevent this, it is common to
inject alcohols or glycols into gas producing wellbores to
prevent plugging with solid hydrates. This injection is
relatively expensive, and further, results in more liquids
being present in the wellbore. Spills of these liquids can
be particular environmental concerns because they are by
nature miscible with water.
Numerous methods and devices exist for separating
components from gaseous or other fluids. Examples of
= CA 02357635 2007-04-12
- 3 -
conventional separation device include distillation
columns, filters and membranes, settling tanks,
centrifuges, electrostatic precipitators, dryers, chillers,
cyclones, vortex tube separators and adsorbers. In
s addition, various inertia separators have been described in
the art, equipped with a supersonic nozzle.
JP-A-02,017,921 refers to the separation of a gaseous
mixture through the use of supersonic flow. The device
includes a swirler positioned upstream of a supersonic
nozzle. The swirling fluid stream then passes through an
axially symmetric expansion nozzle to form fine particles.
The swirl is maintained over a lengthy axial distance,
creating a large pressure drop.
US-A-3,559,373 refers to a supersonic flow separator
including a high pressure gas inlet, a rectangular-shaped
throat, and a U-shaped rectangular cross-sectional channel.
The channel includes an outer curved permeable wall. A gas
stream is provided to the gas inlet at subsonic speeds.
The gas converges through the throat and expands into the
channel, increasing the velocity to supersonic speed. The
expansion of the flow in the supersonic region results in
droplet coalescence and the larger droplets pass through
the outer permeable wall and are collected in a chamber.
EP-A-0,496,128 refers to a method and device for
separating a gas from a gas mixture. The device includes a
cylinder which converges to a nozzle and then diverges into
a swirl zone. Gas enters an inlet port of the cylinder at
subsonic speeds and flows through a converging section of
the nozzle. The flow expands out of the converging section
into the diverging section of the cylinder at supersonic
velocity. A pair of deltoid plates impart a swirl to the
supersonic flow. The combination of the supersonic
velocities and the swirl assist in condensing and
CA 02357635 2007-04-12
- 4 -
separating a condensed component from the gaseous
components of the flow stream. An outlet pipe is
positioned centrally within the cylinder to allow discharge
of the gaseous components of the flow stream at supersonic
velocity. The liquid components continue on through a
second diverging section, which drops the velocity to
subsonic, and through a fan, ultimately exiting the
cylinder through a second outlet.
WO 99/01194 describes a similar method and
corresponding device for removing a selected gaseous
component from a stream of fluid containing a plurality of
gaseous components. This device is equipped with a shock
flow inducer downstream of the collecting zone so as to
decrease the axial velocity of the stream to subsonic
is velocity. Application of a shock wave in this manner
results in a more efficient separation of the formed
particles.
These references describe various supersonic inertia
separators. However, none describe or hint at their use
upstream of a wellhead choke of a well completion system,
and/or instead of the wellhead choke.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a
method for removing condensables from a natural gas stream
upstream of a wellhead choke connected to a subterranean
formation.
More especially, in one aspect of the invention, there
is provided a method for removing condensables from a
natural gas stream upstream of a welihead choke connected
to a subterranean formation using a downhole inertia
separator in which droplets and/or particles are separated
CA 02357635 2007-04-12
- 5 -
from the gases and the gas from which the condensables have
been removed is collected, characterized in that the method
further comprises the steps of:
(A) inducing the natural gas stream to flow at
supersonic velocity through an inertia separator comprising
a conduit having an acceleration section in which the gas
stream is accelerated to a supersonic velocity thereby
causing it to cool to a temperature that is below a
temperature at which condensables will begin to condense
forming separate droplets and/or particles; and
(B) transporting the gas and/or the condensed
condensables to a wellhead and/or re-injecting it into the
subterranean formation from which it has been produced, or
into a different formation, with the proviso that not all
of the collected gas and condensables are re-injected into
the same reservoir zone of the same formation.
In another aspect of the invention, there is provided
a well completion system for producing gas from a
subterranean formation comprising a wellhead, a wellbore
containing a tubing extending downhole from the wellhead,
and an inertia separator comprising
optionally, a swirl imparting section that imparts a
swirling motion to the gas; and
a collection section wherein a gas stream containing
reduced amount of condensables is collected;
characterized in that the inertia separator comprises
an acceleration section wherein in use gas from the
subterranean formation is accelerated to a supersonic
velocity and condensables are condensed.
t . .:
29-01-2001= CA 02357635 2001-06-28 EP 009910497
- 6 -
The invention also concerns a well completion system
for producing gas from a subterranean formation in
accordance with the characterizing features of claim 7.
DETAILED DESCRIPTION OF THE INVENTION
Supersonic inertia separators as referred to herein
before require a predominantly gaseous stream (i.e.
containing less than 10 %wt of either solids or liquids)
at sufficient pressure to undergo supersonic acceleration
when passing through the converging-diverging Laval
nozzle thereof. Pressures in the well and prior to the
wellhead choke can be in the same range as in the
subterranean formation, and are normally more than
adequate. The method can therefore be used in the
wellbore of an unilateral well; in the primary wellbore
or one or more of the branched wellbores of a
multilateral wellbore, or instead of the choke of a
wellhead. The method can therefore be used on the
surface, but also subsurface or sub-sea.
It will be understood that if the supersonic inertia
separator is used instead of a choke, than in an elegant
manner natural gas is freed from condensables at the same
time as the reduction in pressure occurs to the level
required for a distribution network.
One of the more attractive advantages of the present
invention concerns the minimum or even lack of moving
parts in the supersonic inertia separator, allowing the
use thereof at locations that ordinarily require remote
controls. The supersonic inertia separator that is
preferred, is of the type described in EP-A-0,496,128,
i.e., wherein the supersonic stream containing droplets
and/or particles is forced into a swirling motion,
thereby causing the droplets and/or particles to flow to
a radially outer section of a collecting zone in the
stream, followed by the extraction of these droplets
and/or particles in a supersonic collection zone.
AMENDED SHEET
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 7 -
In another preferred embodiment of the present
invention, a shock wave occurs that is caused by
transition from supersonic to subsonic flow upstream of
the separation of the droplets and/or particles from the
collecting zone. It was found that the separation
efficiency is significantly improved if collection of the
particles in the collecting zone takes place after the
shock wave, i.e. in subsonic flow rather than in
supersonic flow. This is believed to be because the shock
wave dissipates a substantial amount of kinetic energy of
the stream and thereby strongly reduces the axial
component of the fluid velocity while the tangential
component (caused by the swirl imparting means) remains
substantially unchanged. As a result the number density
of the particles in the radially outer section of the
collecting zone is significantly higher than elsewhere in
the conduit where the flow is supersonic. It is believed
that this effect is caused by the strongly reduced axial
fluid velocity and thereby a reduced tendency of the
particles to be entrained by a central "core" of the
stream where the fluid flows at a higher axial velocity
than nearer the wall of the conduit. Thus, in the
subsonic flow regime the centrifugal forces acting on the
condensed particles are not to a great extent counter-
acted by the entraining action of the central "core" of
the stream, so that the particles are allowed to
agglomerate in the radially outer section of the
collecting zone from which they are extracted.
Preferably the shock wave is created by inducing the
stream of fluid to flow through a diffuser. A suitable
diffuser is a supersonic diffuser. A diffuser may be, for
example, a diverging volume, or a converging and then
diverging volume.
In an advantageous embodiment, the collecting zone is
located adjacent the outlet end of the diffuser.
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 8 -
The present invention may be practiced in combination
with other operations to effect drying of the fluid
stream, or practicedin front of conventional separators
in order to reduce the size and or capacity required of
the latter. Also, either of the stream containing liquids
from the collecting zone or the stream from which the
liquids have been separated could be subjected to an
additional separation step, for example, a dryer or
separator.
Advantageously, any gaseous fraction separated
together with the condensables, e.g. from the radially
outer section of the collecting zone in case of an
supersonic inertia separator of the type described in EP-
A-0,496,128 or WO 99/011994, can be recycled back to the
inlet, preferably using an inductor to increase the
pressure back to the pressure of the inlet stream.
Another alternative in the practice of the present
invention is to route the condensables to a liquid-liquid
separator, wherein for instance a liquid hydrocarbon
phase is isolated from an aqueous phase. The liquid water
phase could be, for example, re-injected into the same
formation, at a shallower or deeper reservoir zone, or
into a different formation. The liquid hydrocarbon phase
could be produced either with the gases, instead of the
gases, or separately from the gases. Re-injection of the
liquid hydrocarbon phase, e.g. for later production, is
also an option.
Suitably the means for inducing the stream to flow at
supersonic velocity comprises a Laval-type inlet of the
conduit, wherein the smallest cross-sectional flow area
of the diffuser is preferably larger than the smallest
cross-sectional flow area of the Laval-type inlet.
The present invention may also be utilized to re-
inject gas separated from condensables within a wellbore.
For example, when multiple reservoirs are present (for
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 9 -
example, stacked reservoirs or different reservoirs
penetrated by different wellbores of a multilateral well)
and it is desired to produce only condensates from the
gas. Gases may be re-injected to prevent flaring or to
maintain reservoir pressure. A separator of the present
invention could remove condensable fluids from gas, and
the gas could then be re-injected from the same wellbore.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows schematically a longitudinal cross-
section of a first preferred embodiment of the separator
useful in the practice of the present invention.
FIG. 2 shows schematically a longitudinal cross-
section of a second embodiment of the device useful in
the practice of the present invention.
FIG. 3 shows schematically a device according to the
present invention within a wellbore of a well completion
system.
FIG. 4 shows schematically an device used to
demonstrate the device useful in the practice of the
present invention.
FIGS. 5A and 5B show schematically an device
according to the present invention at a wellhead of a
well completion system.
FIG. 6 is a schematic drawing of an embodiment of the
present invention wherein the liquid stream from the
separator of the present invention is routed to a liquid-
liquid separator, and an aqueous phase is separated from
a hydrocarbon phase, and the aqueous phase is re-injected
into a formation.
FIG. 7 is a schematic drawing of an embodiment of the
present invention wherein condensate is produced, and gas
is re-injected into a formation.
DESCRIPTION OF A PREFERRED EMBODIMENT
In Fig. 1 is shown a conduit in the form of an open-
ended tubular housing 1. A fluid inlet 3 is provided at
29-01-2001- CA 02357635 2001-06-28 EP 009910497
- 10 -
one end of the housing, a first outlet 5 for liquid laden
fluid near the other end of the housing, and a second
outlet 7 for substantially liquid-free fluid at the other
end of the housing. The flow-direction in the device 1 is
from the inlet 3 to the first and second outlets 5, 7.
The inlet 3 is an acceleration section containing a
Laval-type, having a longitudinal cross-section of
converging-diverging shape in the flow direction so as to
induce a supersonic flow velocity to a fluid stream which
is to flow into the housing via said inlet 3. The housing
1 is further provided with a primary cylindrical part 9
and a diffuser 11 whereby the primary cylindrical part 9
is located between the inlet 3 and the diffuser 11. One
or more (for example, four) delta-shaped wings 15 project
radially inward from the inner surface of the primary
cylindrical part 9, each wing 15 being arranged at a
selected angle to the flow-direction in the housing so as
to impart a swirling motion to fluid flowing at
supersonic velocity through the primary cylindrical
part 9 of the housing 1.
The diffuser 11 has a longitudinal section of
converging - diverging shape in the flow direction,
defining a diffuser inlet 16 and a diffuser outlet 19.
The smallest cross-sectional flow area of the diffuser is
larger than the smallest cross-sectional flow area of the
Laval-type inlet 3.
The housing 1 further includes a secondary
cylindrical part 17 having a larger flow area than the
primary cylindrical part 9 and being arranged downstream
the diffuser 11 in the form of a continuation of the
diffuser 11. The secondary cylindrical part 17 is
provided with longitudinal outlet slits 18 for liquid,
which slits 18 are arranged at a suitable distance from
the diffuser outlet 19.
AMENDED SHEET
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 11 -
An outlet chamber 21 encloses the secondary
cylindrical part 17, and is provided with the afore-
mentioned first outlet 5 for a stream of concentrated
liquids.
The secondary cylindrical part 17 debouches into the
aforementioned second outlet 7 for substantially gas.
Normal operation of the device 1 is now explained for
the embodiment using subsonic separation.
A stream containing micron-sized particles is
introduced into the Laval-type inlet 3. As the stream
flows through the inlet 3, the stream is accelerated to
supersonic velocity. As a result of the strongly
increasing velocity of the stream, the temperature and
pressure of the stream may decrease to below the
condensation point of heavier gaseous components of the
stream (for example, water vapors) which thereby condense
to form a plurality of liquid particles. As the stream
flows along the delta-shaped wings 15 a swirling motion
is imparted to the stream (schematically indicated by
spiral 22) so that the liquid particles become subjected
to radially outward centrifugal forces. When the stream
enters the diffuser 11 a shock wave is created near the
downstream outlet 19 of the diffuser 11. The shock wave
dissipates a substantial amount of kinetic energy of the
stream, whereby mainly the axial component of the fluid
velocity is decreased. As a result of the strongly
decreased axial component of the fluid velocity, the
central part of the stream (or "core") flows at a reduced
axial velocity. This results in a reduced tendency of the
solids and condensed particles to be entrained by the
central part of the stream flowing in the secondary
cylindrical part 17. The condensed particles can
therefore agglomerate in a radially outer section of a
collecting zone of the stream in the secondary
cylindrical part 17. The agglomerated particles form a
_ .~
29-01-2001' CA 02357635 2001-06-28 EP 009910497
- 12 -
layer of liquid which is extracted from the collecting
zone via the outlet slits 18, the outlet chamber 21, and
the first outlet 5 for substantially liquid. It is,
however, also within the spirit of this invention to
remove the condensed particles at supersonic velocity,
without an upstream shock wave.
The stream from which condensable vapors have been
removed is discharged through the second outlet 7 for
substantially liquid-free gas.
In Fig. 2 is shown a second embodiment of the device
for carrying out the invention. This device has an open-
ended tubular housing 23 with a Laval-type fluid inlet 25
at one end and a first outlet 27 for stream containing
the solids and any condensed liquid at the other end of
the housing. The flow-direction for fluid in the device
is indicated by arrow 30. The housing has, from the inlet
to the liquid outlet 27, a primary substantially
cylindrical part 33, a diverging diffuser 35, a secondary
cylindrical part 37 and a diverging part 39. A delta-
20 shaped wing 41 projects radially inward in the primary
cylindrical part 33, the wing 41 being arranged at a
selected angle to the flow-direction in the housing so as
to impart a swirling motion to fluid flowing at
supersonic velocity through the housing 23. A tube-shaped
25 second outlet 43 for substantially gas extends through
the first outlet 27 co-axially into the housing, and has
an inlet opening 45 at the downstream end of the
secondary cylindrical part 37. The outlet 43 may be
internally provided with a straightened (not shown), e.g.
a vane-type straightener, for transferring swirling flow
of the gas into straight flow.
Normal operation of the second embodiment is
substantially similar to normal operation of the first
embodiment. Supersonic swirling flow occurs in the
primary cylindrical part 33 and a shock wave, if any,
AMENDED SHEET
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 13 -
occurs near the transition of the diffuser 35 to the
secondary cylindrical part 37. Subsonic flow occurs if a
diffuser is used in the secondary cylindrical part 37.
The stream containing the solid particles and any
condensed liquids is discharged through the first outlet
27, and the dried gas is discharged through the second
outlet 43 in which the swirling flow of the gas is
transferred into straight flow by the straightener.
In the above detailed description, the housing, the
primary cylindrical part, the diffuser and the secondary
cylindrical part have a circular cross-section. However,
any other suitable cross-section of each one of these
items can be selected. Also, the primary and secondary
parts can alternatively have a shape other than
cylindrical, for example a frusto-conical shape. Further-
more, the diffuser can have any other suitable shape, for
example without a converging part (as shown in Fig. 2)
especially for applications at lower supersonic fluid
velocities.
Instead of each wing being arranged at a fixed angle
relative to the axial direction of the housing, the wing
can be arranged at a changing angle with respect to the
direction of flow, preferably in combination with a
spiraling shape of the wing. A similar result can be
obtained by arranging flat wings along a path of
increasing angle with respect to the axis of initial
flow.
Furthermore, each wing can be provided with a raised
wing-tip (also referred to as a winglet).
Instead of the diffuser having a diverging shape
(Fig. 2), the diffuser alternatively has a diverging
section followed by a converging section when seen in the
flow direction. An advantage of such diverging-converging
shaped diffuser is that less fluid temperature increase
occurs in the diffuser.
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 14 -
Referring now to FIG. 3, an device of the present
invention is shown in a wellbore. A formation from which
hydrocarbons are being produced 301 is below an
overburden 302, and is penetrated by a wellbore 303. The
wellbore provides communication from the formation
through perforations 305 which are shown as packed with
sand 306 to prevent collapse of the formation into the
perforations. A casing 307 is placed in the wellbore and
secured with cement 308 that is placed by circulation
from the inside of the casing and out the outside to
provide support. The cement is followed by a cement plug
309 that remains in the bottom of the casing, and is
caught by a lip 310 provided in the bottom segment of
casing for that purpose.
Gas flowing from the formation is forced through the
separator of the present invention by a sealing packer
311 that is effective to isolate the wellbore in the
region of the producing formation. Gas from the producing
formation goes through the inlet Laval nozzle 312 where
supersonic velocities are created, and wing 313 induces a
swirl to the supersonic flow. A sufficiently long flow
path 314 is provided for the supersonic flow region. A
diffuser section 315, if any, is provided to create a
sonic shock wave, preferably just upstream of the
separation of the liquids from the radially outer section
from the vapors, which are captured in a vortex finder
316 and routed to the surface through a production tubing
317. Flow from the radially outer section of portion of
the collection section 318 is shown as being routed to
the outside of the production tubing to an annular volume
between the casing 307 and the production tubing 317 by
way of a tangential outlet 319. The tangential outlet can
help separate liquids from the vapors in the liquid
stream. Although the stream being removed from the
radially outer section of the collection section is
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 15 -
initially liquid, considerable vaporization may occur as
the gas is re-compressed in the shock wave induced by the
diffuser. But the liquid could be sufficiently
concentrated that even this rise in temperature does not
vaporize all of the condensables in the stream. A typical
sucker-rod pump or downhole electrical pump 320 is shown
to remove liquid water that has fallen back to the
isolation packer 311. Re-injection into the formation is
also possible, both for liquids and gases, possibly with
the help of electric submersible pumps if required by the
formation pressure regime or in case of multilateral
wells.
The stream concentrated in water and/or heavy
hydrocarbons is preferably of such a composition that
addition of components to prevent formation of hydrates
is not needed. Even if hydrate inhibition is desirable,
the amount of hydrate inhibition compound needed will be
considerably reduced because of the need to treat only
the smaller volume of fluid to be treated.
Referring now to FIG. 5A, a device of the present
invention is shown schematically at a sub-sea wellhead. A
sub-sea well 501, in a body of water 513 is shown with a
casing 502, with perforations 503 providing communication
from a formation 512 to the inside of the wellbore 504.
Typical well head equipment 505 is schematically shown.
The separator of the present invention 506 separates a
mostly liquid stream 507 from a dried stream of vapors
508. Temperatures at the sea floor 509 approach freezing
temperatures, and formation of hydrates along sea floor
piping is therefore a serious concern. The present
invention provides a simple, low maintenance and
inexpensive dehydration system. The separated liquids may
be provided with hydrate inhibition additive 510 through
a controlled injection 511.
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 16 -
Referring now to FIG. 5B, another embodiment is
shown, with a wellbore 550 located at a surface 551. The
wellbore is cased with a casing 554 provided with
perforations 555. Typical wellhead equipment may be
provided 552. A liquid-vapor separator 553 is provided
with a liquid outlet 556 and a level control system 557.
A vapor outlet from the liquid-vapor separator 563 is
routed to the dehydrator of the present invention 558.
The vapors from the outlet 559 of the separator of the
present invention is dry gas 560 having a dew point lower
than the dew point of the produced gases. Liquid from the
separator of the present invention 564 may contain
vapors, which will be saturated, and are therefore
preferably routed to a second vapor-liquid separator 561.
The liquids from this second separator 562 can be
combined with liquids from the first separator, or routed
separately to surface equipment. Alternatively, liquids
from the second separator may be re-injected into a
formation for effective disposal. The liquids from the
second separator may be pumped to a higher pressure
reservoir, which may be connected via a different
wellbore of a multilateral well, or flow by pressure drop
available to a low pressure formation. The liquids from
the second separator, if re-injection is desirable, may
be collected and then re-injected, or re-injected into
the wellbore from which the gas was produced.
Referring now to FIG. 6, an embodiment of the present
invention is shown wherein a separator of the present
invention 601 is within a wellbore 602 that is perforated
in a hydrocarbon gas producing formation 603. The
wellbore is shown as cased with a casing 604 that is
cemented with cement 605, with a cement shoe 606. A
packer 607 isolates the producing portion of the
wellbore, forcing the produced gas into an inlet 608 to
the separator of the present invention. A wing 609
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 17 -
induces a swirl to the supersonic gases that have passed
through the Laval nozzle 610, and condensables are
collected and exit the separator from a liquid outlet
611. Liquids from the liquid outlet pass to a liquid-
liquid separator 612. The liquid-liquid separator can be
any kind known in the art. The liquids are separated into
a hydrocarbon phase, which is routed to a wellhead 613 at
the surface 614, through a tubing 618 such as a coiled
tubing. A liquid aqueous phase 615 which is routed
through perforations 616 to a formation. A second set of
packers 619 is shown as isolating a section of the
wellbore for re-injection of the aqueous phase. Vapor
from which the condensables including water have been
removed are routed through a production tubing 617 to the
wellhead where produced gas 620 and produced hydrocarbon
liquids 621 are gathered separately.
Referring now to FIG. 7, a wellbore 701 is shown with
a casing 714 perforated by perforations 702. Cement 703
secures the casing in a formation 704 from which
hydrocarbons are produced, the cement having been forced
down the casing by pressure behind a cement shoe 715. The
hydrocarbons are forced through a separator 705 of the
present invention. The separator of the present invention
has a liquid outlet 706 and a vapor outlet 707. The
liquid outlet is in communication with a production
tubing 708. The vapor outlet is in communication with a
segment of the volume inside the casing 709 that is in
communication with a second formation 710 to which the
vapors are to be re-injected through more perforations
711. The segment of the volume inside of the casing in
communication with the second formation is isolated by
and upper packer 712 and a lower packer 713.
Not shown is the use of a device as described in
either FIG. 6 or 7, in a multiple branched wellbore
system. If used in a branched wellbore system, the device
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 18 -
is preferably used at the conjunction point of the
wellbores. In such arrangement the, or part of the
condensable, or instead the, or part of the treated gas
stream may be directed via the branch wellbore to either
a different formation or a different reservoir zone. Such
a system would be used, for example, to avoid water
production to the surface, which would require further
processing. It may also be used to flow gas to a
reservoir zone used for pressure maintenance or
underground gas storage.
The swirl imparting means can be arranged at the
inlet part of the conduit, instead of downstream the
inlet part.
EXAMPLE
A test device for the present invention was prepared,
and demonstrated for separating water vapor from air at
ambient conditions. Obviously, in case the device is used
subsurface, sub-sea or at the wellhead, different
temperatures pressures and Mach numbers may apply.
However, a skilled man will have no difficulty making the
necessary adaptations. Fig. 4 is referred to for the
general configuration of the device used.
In this example the air 425 was pressurized to
140 KPa (1.4 bar (a)) by means of a blower 401 to provide
pressurized air 426. After the blower the air was cooled
to about 25 to 30 C by fin cooler 402, located in a
vessel 418, and water 419 was sprayed into the vapor
space below the cooler 420 to ensure that the air was
near water saturation (RV = 90%). This water saturated
air 427 was fed to the feed liquid-vapor separator 403
where the water was separated with a small amount of slip
air into a wet stream 421, coming along with this water
liquid stream and dried air 422.
In this example, the device was provided with tubular
flow ducts although the same results can be achieved for
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 19 -
rectangular or asymmetric duct cross sections. Therefore
diameters of devices are mentioned and always refer to
the inner diameter.
The typical inlet conditions are summarized below:
1. Mass flow rate . 1.2 kg/s
2. Inlet pressure . 140 KPa (1400 mbar (a))
3. Inlet temperature . 25 C
4. Inlet humidity . 90%
The device condensed water vapor, resulting in a mist
flow containing large number of water droplet. The final
temperature and pressure in the supersonic zone 428 were
found to be -28 C and 68 KPa (680 mbar (a) ) , resulting
in a water vapor fraction that was negligibly small.
The nozzle throat diameter 404 was 70 mm. The inlet
diameter 405 was 300 mm, although its value is not
significant with respect to the working of the device.
The nozzle outlet diameter 400 was 80 mm in order to
obtain supersonic flow conditions; typically the
corresponding Mach number, M = 1.15.
The lengths of the nozzle are determined by the
cooling speed, which for this case is 19000 K/s. Persons
of ordinary skill in the art can determine pressure and
temperature profiles for the flow through the device, and
thus the cooling rate. The cooling speed determines the
droplet size distribution. Lowering the value of the
cooling speed results in larger average droplet sizes.
The lengths of the nozzle were:
L1, 406 : 700 mm : from nozzle inlet to nozzle throat
L2, 407 : 800 mm : from nozzle throat to nozzle outlet
In order to decrease frictional losses the wall
roughness was small, preferably 1 micron or less.
Depending on the application any rigid material can
be used for the nozzle device, as long as the before
mentioned design parameters are respected.
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 20 -
The vortex tube 408 was connected between the nozzle
outlet and the diffuser. In the vortex tube a wing-like,
swirl imparting internal 409 was present. At the edge of
this internal a vortex was created on the upper (low-
pressure) side and shed from the plane, preferably at the
trailing edge. The root cord of this wing-like plate was
attached to the inner wall of the vortex tube.
The inlet diameter of the vortex tube 400 was 80 mm.
In this case vortex tube was slightly conical; the
diameter increased linearly to 84 mm (423) over a length
of approximately the cord length of the wing.
After the conical section of the vortex tube 410, the
vortex tube diameter was constantly 84 mm over a length
were the droplets deposited on the inner wall (separation
length). These two lengths were:
L3, 410 : 300 mm : from wing apex to wing trailing edge
L4, 412 : 300 mm : from wing trailing edge to diffuser
The sizing of the wing internal depended on the
preferred circulation or integral vorticity. This
circulation is typical 16 m2/s resulting from a wing cord
length of 300 mm, a wing span at the trailing edge of
60 mm and at an incidence of the wing cord at the axis of
the tube of 8 . The sweepback angle of the leading edge
(from perpendicular to the flow) was 87 and the
sweepback angle of the trailing edge was 40 . The edges
of the wing were sharp. The plane of the wing was flat
and its profile was extremely slender. The thickness of
the wing was about 4 mm at the root. The wing was at an
8 angle to the axis of the tube.
In the drainage section withdrawal of liquids out of
the vortex tube was achieved. The drainage section is not
a sharp distinguished device but is an integral part of
the vortex tube, by means of, for example, slits, porous
materials, holes in the vortex tube walls; or, as shown
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 21 -
in FIG. 4, is an integral part of the diffuser by means
of a vortex finder 413 (co-axial duct). In this example,
a vortex finder (co-axial duct) was placed centrally in
the duct after the shock wave, which was present directly
after the vortex tube in the first diffuser part 414.
The sizing of the vortex tube is dependent on the
diameter ratio between diffuser diameter at that location
424 (90 mm at the inlet) and vortex finder inlet diameter
at that point 425 (85 mm at the inlet). The cross-
sectional area difference between the latter two
influences the minimal flow, which is extracted from the
main stream containing the liquids. In this case this
minimal flow was 100 of the main flow i.e. 0.12 kg/s. The
diffuser length 433 was 1500 mm.
In the diffuser the remaining kinetic energy in the
flow is transformed to potential energy (increase of
static pressure). It is desirable to avoid boundary layer
separation, which can cause stall resulting in a low
efficiency. Therefore the half divergence angle of the
diffuser in the present test set-up should be preferably
less then 5 as in this case 4 was used. The diffuser
inlet diameter was the same as the vortex finder inlet
diameter (85 mm). The outlet diameter 415 of the diffuser
was 300 mm, and the dry air at this point was at about
atmospheric pressure. The performance of this device was
measured by two humidity sensors (capacitive principle:
manufacturer 'Vaisala') one at the air inlet 416 and the
other at the dried air outlet 417, both were corrected
for temperature and pressure. The typical values of the
inlet water fractions were 18-20 gram of water vapor per
kg dry air. Typical values of the outlet water were 13-15
gram of water vapor per kg dry air. This can be expressed
in separation efficiencies of about 25% of the water
vapor in the inlet removed. This also corresponds to the
separation of liquids condensed in the super sonic
CA 02357635 2001-06-28
WO 00/40835 PCT/EP99/10497
- 22 -
region, because most of the liquid water present in the
inlet stream condenses at that point.
